A review on nocturnal surface ozone enhancement: Characterization, formation causes, and atmospheric chemical effects

In recent years, the frequent occurrence of nocturnal background ozone enhancement (A gradually increasing trend in the long-term change of nocturnal ozone concentration, [NBOE]) and nocturnal ozone enhancement (the presence of a nocturnal ozone peak and high nocturnal ozone value, [NOE]) have attracted extensive attention in the academic community. NBOE and NOE impact atmospheric chemical processes, and higher nocturnal ozone concentrations adversely affect human health and biological growth. Therefore, we reviewed the research history of NBOE and NOE, provided an overview of research on NBOE, and summarized the spatiotemporal distribution characteristics of NOE. According to the available observations, the frequency of NOE in a long-time series (i.e., more than one year) from 2005 to 2020 generally ranges between 15 % and 50 %. Compared to other nations, China has a higher nocturnal ozone peak. In most NOE events, the magnitude of ozone increase (ΔO₃/Δt) ranges from 5 to 20 ppb, and NOE events occur more frequently during midnight. In addition, we described the current international-level understanding of the causes of NOE and the impact of NOE on nighttime and next-day atmospheric chemical processes. Future research should not only enhance the quantitative analysis of the causal factors of NBOE and NOE, but also prioritize exploring how NBOE and NOE influence secondary pollutant production, human health, and biological growth. Finally, attention should be paid to the influence of NBOE and NOE on the formulation of synergistic control policies for PM_2.5 and ozone.